The application of non-invasive ventilation (“NIV”) to a patient in need of respiratory support provides the patient with benefits over the use of invasive ventilation techniques such as with an endotracheal (ET) tube. NIV reduces the trauma that a patient experiences in the application of invasive ventilation techniques, for example, intubation. The use of NIV also reduces the risk of ventilator-associated pneumonia and facilitates the weaning of a patient off of mechanical ventilation. Many types of patient interfaces exist to provide a patient with non-invasive ventilation, the most common interfaces utilize a version of a face mask. A drawback of patient interfaces that utilize a face mask is that the patient's mouth is blocked. This reduces the patient's ability to communicate. Furthermore a face mask makes it difficult for the patient to ingest nutrition and/or medication. Also, in the event that a patient vomits, a face mask presents an increased risk of a blocked airway. Finally, patients find discomfort with the use of a mask, both due to the blockage of the patient's mouth as well as the pneumatic pressure that is applied to the patient's face through the patient interface.
In order to address these issues, a pneumatic helmet has been used to deliver respiratory support to a patient. The helmet secures around the patient's neck and/or shoulders to provide a pneumatically sealed compartment about the patient's head. The helmet is typically constructed of a flexible and transparent material such that the patient retains the freedom to move his or her head and to communicate verbally and non-verbally through the material of the helmet. The benefits of the helmet include improved patient communication and a greater sense of freedom experienced by the patient.
However, it has been identified that the noise within the confined space of a non-invasive ventilation helmet can reach discomforting and even dangerous levels. Studies have measured the noise inside the helmet to exceed 100 dB. While OSHA workplace safety standards suggest limiting exposure to noises above 100 dB to less than 2 hours at a time, the patient may be exposed to these noise levels throughout the duration of the respiratory support, which may last days or weeks. This compounds any ill effects from the exposure to the loud noises. The loud noises also contribute to the discomfort that the patient associates with receiving respiratory support. Patient discomfort can lead to an overall unfavorable care experience, and can lead to adverse physiological effects such as increased heart rate or blood pressure. Furthermore excessive noise in the helmet may prevent the patient from falling asleep, and/or staying asleep, thereby reducing the patient's ability to recuperate.
The noise within the helmet has many sources within the mechanical ventilator. One source of noise is the medical gas supply source. Mechanical ventilators typically have one of two different types of systems for providing a flow of medical gas. First, the flow of medical gas may be generated by a compressor or pump that takes in ambient air and delivers it at the desired flow rate to the patient. This compressor or pump is typically loud in its operation, resulting in this noise being transmitted to the helmet. Secondly, the flow of medical gas may be received by the mechanical ventilator from a wall supply of high pressure medical gas supplied to the hospital room. In this system, a pressure regulator in the ventilator reduces the wall gas pressure to deliver a flow of medical gas at the desired flow rate. The reduction of the wall gas pressure is loud and this noise is transmitted through the breathing circuit directly to the patient via the helmet. Therefore, both sources of medical gas commonly used by medical ventilators cause noise in the NIV helmet. Alternatively, the flow of medical gas may be supplied by a different apparatus such as a stand alone CPAP device, or a manual ventilation bag. However, the noise within the patient interface is also an issue with these sources of medical gas flow. Furthermore, it is not uncommon for the plastic tubing that forms the breathing circuit to be corrugated in design to promote flexibility and reduce kinking. However, the corrugated tubing causes turbulence in the flow of medical gas, therefore creating additional noise in the breathing circuit and the NIV helmet.
Attempts have been made to reduce the noise levels within the helmet by modifying the pressure and flow rates of the medical gases provided to the patient through the helmet. However, this technique has not shown a meaningful effect on reducing the noise within the helmet. Alternatively, it has been attempted to reduce the noise in the helmet by including one or more filters, such as a heat and moisture exchange (HME) filter, in an attempt to attenuate the noise associated with the provision of medical gas to the helmet. However, this too did not produce a meaningful decrease in the noise experienced inside of the helmet.
The lack of effectiveness of these attempts to reduce noise may be due to the fact that the noise is the result of inherent features of standard mechanical ventilator components. Furthermore, the HME filter is not designed to maximize any sound-attenuating properties that the HME filter may have. While a HME filter comprises a core of foam or other filter material that the medical gas must flow through, the amount of material present is not sufficient to dampen the noise effectively. If the filter material of the HME filter were modified or the amount of the filter material increased, the HME filter would present an increased resistance to the flow of medical gas being provided to the patient. Increased resistance within the breathing circuit of a mechanical ventilation system is undesirable as this resistance must be overcome by higher pressures within the breathing circuit and the resistance affects the waveform of medical gas that is actually received by the patient.
Therefore, it is desirable in the field of non-invasive mechanical ventilation to provide a sound dampening apparatus for a mechanical ventilation system such that the sound dampening apparatus reduces the noise within a non-invasive helmet and does not substantially increase the resistance of the breathing circuit.